package online.heycm.platform.common.entity.result;

import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Stream;

/**
 * java.util.Optional 扩展
 *
 * @author heycm
 * @since 2022/6/4 13:47
 */
public class Optional<T> {

    /**
     * Common instance for empty().
     */
    private static final Optional<?> EMPTY = new Optional<>(null);

    /**
     * If non-null, the value; if null, indicates no value is present
     */
    private final T value;

    /**
     * if no value present, codeMsg for desc.
     */
    private ErrorCode errorCode;

    /**
     * Returns an empty {@code Optional} instance with fail message.  No value is present for this {@code Optional}.
     *
     * @param <T>     The type of the non-existent value
     * @param message fail message
     * @return an empty {@code Optional}
     */
    public static <T> Optional<T> error(String message) {
        Optional<T> t = new Optional<>(null);
        t.errorCode = new ErrorCode() {
            @Override
            public int code() {
                return 0;
            }

            @Override
            public String message() {
                return message;
            }
        };
        return t;
    }

    /**
     * Returns an empty {@code Optional} instance with fail code and message.  No value is present for this {@code
     * Optional}.
     *
     * @param <T>     The type of the non-existent value
     * @param code    fail code
     * @param message fail message
     * @return an empty {@code Optional}
     */
    public static <T> Optional<T> error(int code, String message) {
        Optional<T> t = new Optional<>(null);
        t.errorCode = new ErrorCode() {
            @Override
            public int code() {
                return code;
            }

            @Override
            public String message() {
                return message;
            }
        };
        return t;
    }

    /**
     * Returns an empty {@code Optional} instance with fail codeMsg.  No value is present for this {@code Optional}.
     *
     * @param <T>     The type of the non-existent value
     * @param errorCode fail codeMsg
     * @return an empty {@code Optional}
     */
    public static <T> Optional<T> error(ErrorCode errorCode) {
        Optional<T> t = new Optional<>(null);
        t.errorCode = errorCode;
        return t;
    }

    /**
     * Returns an {@code Optional} instance after clear <?>.
     *
     * @param <T>      The type of the non-existent value
     * @param optional fail message
     * @return an {@code Optional}
     */
    public static <T> Optional<T> error(Optional<?> optional) {
        @SuppressWarnings("unchecked")
        Optional<T> t = (Optional<T>) optional;
        return t;
    }

    public static Optional<Boolean> success() {
        return Optional.of(Boolean.TRUE);
    }

    public static <T> Optional<T> ifFail(boolean ok, ErrorCode errorCode) {
        return ok ? (Optional<T>) success() : error(errorCode);
    }

    public static <T> Optional<T> ifFail(boolean ok, String message) {
        return ok ? (Optional<T>) success() : error(message);
    }

    public static <T> Optional<T> ifFail(boolean ok, int code, String message) {
        return ok ? (Optional<T>) success() : error(code, message);
    }

    /**
     * Returns the fail message.
     *
     * @return fail message
     */
    public String message() {
        return errorCode.message();
    }

    public int code() {
        return errorCode.code();
    }

    public ErrorCode error() {
        return errorCode;
    }

    /**
     * {@link #isEmpty()}
     */
    public boolean fail() {
        return isEmpty();
    }

    /**
     * Returns an empty {@code Optional} instance.  No value is present for this {@code Optional}.
     *
     * @param <T> The type of the non-existent value
     * @return an empty {@code Optional}
     * @apiNote Though it may be tempting to do so, avoid testing if an object is empty by comparing with {@code ==} or
     * {@code !=} against instances returned by {@code Optional.empty()}.  There is no guarantee that it is a singleton.
     * Instead, use {@link #isEmpty()} or {@link #isPresent()}.
     */
    public static <T> Optional<T> empty() {
        @SuppressWarnings("unchecked")
        Optional<T> t = (Optional<T>) EMPTY;
        return t;
    }

    /**
     * Constructs an instance with the described value.
     *
     * @param value the value to describe; it's the caller's responsibility to ensure the value is non-{@code null}
     *              unless creating the singleton instance returned by {@code empty()}.
     */
    private Optional(T value) {
        this.value = value;
    }

    /**
     * Returns an {@code Optional} describing the given non-{@code null} value.
     *
     * @param value the value to describe, which must be non-{@code null}
     * @param <T>   the type of the value
     * @return an {@code Optional} with the value present
     * @throws NullPointerException if value is {@code null}
     */
    public static <T> Optional<T> of(T value) {
        return new Optional<>(Objects.requireNonNull(value));
    }

    /**
     * Returns an {@code Optional} describing the given value, if non-{@code null}, otherwise returns an empty {@code
     * Optional}.
     *
     * @param value the possibly-{@code null} value to describe
     * @param <T>   the type of the value
     * @return an {@code Optional} with a present value if the specified value is non-{@code null}, otherwise an empty
     * {@code Optional}
     */
    @SuppressWarnings("unchecked")
    public static <T> Optional<T> ofNullable(T value) {
        return value == null ? (Optional<T>) EMPTY
                : new Optional<>(value);
    }

    /**
     * If a value is present, returns the value, otherwise throws {@code NoSuchElementException}.
     *
     * @return the non-{@code null} value described by this {@code Optional}
     * @throws NoSuchElementException if no value is present
     * @apiNote The preferred alternative to this method is {@link #orElseThrow()}.
     */
    public T get() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }

    /**
     * If a value is present, returns {@code true}, otherwise {@code false}.
     *
     * @return {@code true} if a value is present, otherwise {@code false}
     */
    public boolean isPresent() {
        return value != null;
    }

    /**
     * If a value is  not present, returns {@code true}, otherwise {@code false}.
     *
     * @return {@code true} if a value is not present, otherwise {@code false}
     * @since 11
     */
    public boolean isEmpty() {
        return value == null;
    }

    /**
     * If a value is present, performs the given action with the value, otherwise does nothing.
     *
     * @param action the action to be performed, if a value is present
     * @throws NullPointerException if value is present and the given action is {@code null}
     */
    public void ifPresent(Consumer<? super T> action) {
        if (value != null) {
            action.accept(value);
        }
    }

    /**
     * If a value is present, performs the given action with the value, otherwise performs the given empty-based
     * action.
     *
     * @param action      the action to be performed, if a value is present
     * @param emptyAction the empty-based action to be performed, if no value is present
     * @throws NullPointerException if a value is present and the given action is {@code null}, or no value is present
     *                              and the given empty-based action is {@code null}.
     * @since 9
     */
    public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction) {
        if (value != null) {
            action.accept(value);
        } else {
            emptyAction.run();
        }
    }

    /**
     * If a value is present, and the value matches the given predicate, returns an {@code Optional} describing the
     * value, otherwise returns an empty {@code Optional}.
     *
     * @param predicate the predicate to apply to a value, if present
     * @return an {@code Optional} describing the value of this {@code Optional}, if a value is present and the value
     * matches the given predicate, otherwise an empty {@code Optional}
     * @throws NullPointerException if the predicate is {@code null}
     */
    public Optional<T> filter(Predicate<? super T> predicate) {
        Objects.requireNonNull(predicate);
        if (!isPresent()) {
            return this;
        } else {
            return predicate.test(value) ? this : empty();
        }
    }

    /**
     * If a value is present, returns an {@code Optional} describing (as if by {@link #ofNullable}) the result of
     * applying the given mapping function to the value, otherwise returns an empty {@code Optional}.
     *
     * <p>If the mapping function returns a {@code null} result then this method
     * returns an empty {@code Optional}.
     *
     * @param mapper the mapping function to apply to a value, if present
     * @param <U>    The type of the value returned from the mapping function
     * @return an {@code Optional} describing the result of applying a mapping function to the value of this {@code
     * Optional}, if a value is present, otherwise an empty {@code Optional}
     * @throws NullPointerException if the mapping function is {@code null}
     * @apiNote This method supports post-processing on {@code Optional} values, without the need to explicitly check
     * for a return status.  For example, the following code traverses a stream of URIs, selects one that has not yet
     * been processed, and creates a path from that URI, returning an {@code Optional<Path>}:
     *
     * <pre>{@code
     *     Optional<Path> p =
     *         uris.stream().filter(uri -> !isProcessedYet(uri))
     *                       .findFirst()
     *                       .map(Paths::get);
     * }</pre>
     * <p>
     * Here, {@code findFirst} returns an {@code Optional<URI>}, and then {@code map} returns an {@code Optional<Path>}
     * for the desired URI if one exists.
     */
    public <U> Optional<U> map(Function<? super T, ? extends U> mapper) {
        Objects.requireNonNull(mapper);
        if (!isPresent()) {
            return empty();
        } else {
            return Optional.ofNullable(mapper.apply(value));
        }
    }

    /**
     * If a value is present, returns the result of applying the given {@code Optional}-bearing mapping function to the
     * value, otherwise returns an empty {@code Optional}.
     *
     * <p>This method is similar to {@link #map(Function)}, but the mapping
     * function is one whose result is already an {@code Optional}, and if invoked, {@code flatMap} does not wrap it
     * within an additional {@code Optional}.
     *
     * @param <U>    The type of value of the {@code Optional} returned by the mapping function
     * @param mapper the mapping function to apply to a value, if present
     * @return the result of applying an {@code Optional}-bearing mapping function to the value of this {@code
     * Optional}, if a value is present, otherwise an empty {@code Optional}
     * @throws NullPointerException if the mapping function is {@code null} or returns a {@code null} result
     */
    public <U> Optional<U> flatMap(Function<? super T, ? extends Optional<? extends U>> mapper) {
        Objects.requireNonNull(mapper);
        if (!isPresent()) {
            return empty();
        } else {
            @SuppressWarnings("unchecked")
            Optional<U> r = (Optional<U>) mapper.apply(value);
            return Objects.requireNonNull(r);
        }
    }

    /**
     * If a value is present, returns an {@code Optional} describing the value, otherwise returns an {@code Optional}
     * produced by the supplying function.
     *
     * @param supplier the supplying function that produces an {@code Optional} to be returned
     * @return returns an {@code Optional} describing the value of this {@code Optional}, if a value is present,
     * otherwise an {@code Optional} produced by the supplying function.
     * @throws NullPointerException if the supplying function is {@code null} or produces a {@code null} result
     * @since 9
     */
    public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier) {
        Objects.requireNonNull(supplier);
        if (isPresent()) {
            return this;
        } else {
            @SuppressWarnings("unchecked")
            Optional<T> r = (Optional<T>) supplier.get();
            return Objects.requireNonNull(r);
        }
    }

    /**
     * If a value is present, returns a sequential {@link Stream} containing only that value, otherwise returns an empty
     * {@code Stream}.
     *
     * @return the optional value as a {@code Stream}
     * @apiNote This method can be used to transform a {@code Stream} of optional elements to a {@code Stream} of
     * present value elements:
     * <pre>{@code
     *     Stream<Optional<T>> os = ..
     *     Stream<T> s = os.flatMap(Optional::stream)
     * }</pre>
     * @since 9
     */
    public Stream<T> stream() {
        if (!isPresent()) {
            return Stream.empty();
        } else {
            return Stream.of(value);
        }
    }

    /**
     * If a value is present, returns the value, otherwise returns {@code other}.
     *
     * @param other the value to be returned, if no value is present. May be {@code null}.
     * @return the value, if present, otherwise {@code other}
     */
    public T orElse(T other) {
        return value != null ? value : other;
    }

    /**
     * If a value is present, returns the value, otherwise returns the result produced by the supplying function.
     *
     * @param supplier the supplying function that produces a value to be returned
     * @return the value, if present, otherwise the result produced by the supplying function
     * @throws NullPointerException if no value is present and the supplying function is {@code null}
     */
    public T orElseGet(Supplier<? extends T> supplier) {
        return value != null ? value : supplier.get();
    }

    /**
     * If a value is present, returns the value, otherwise throws {@code NoSuchElementException}.
     *
     * @return the non-{@code null} value described by this {@code Optional}
     * @throws NoSuchElementException if no value is present
     * @since 10
     */
    public T orElseThrow() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        }
        return value;
    }

    /**
     * If a value is present, returns the value, otherwise throws an exception produced by the exception supplying
     * function.
     *
     * @param <X>               Type of the exception to be thrown
     * @param exceptionSupplier the supplying function that produces an exception to be thrown
     * @return the value, if present
     * @throws X                    if no value is present
     * @throws NullPointerException if no value is present and the exception supplying function is {@code null}
     * @apiNote A method reference to the exception constructor with an empty argument list can be used as the supplier.
     * For example, {@code IllegalStateException::new}
     */
    public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
        if (value != null) {
            return value;
        } else {
            throw exceptionSupplier.get();
        }
    }

    /**
     * Indicates whether some other object is "equal to" this {@code Optional}. The other object is considered equal
     * if:
     * <ul>
     * <li>it is also an {@code Optional} and;
     * <li>both instances have no value present or;
     * <li>the present values are "equal to" each other via {@code equals()}.
     * </ul>
     *
     * @param obj an object to be tested for equality
     * @return {@code true} if the other object is "equal to" this object otherwise {@code false}
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }

        if (obj instanceof  Optional) {
            Optional<?> other = (Optional<?>) obj;
            return Objects.equals(value, other.value);
        }

        return false;
    }

    /**
     * Returns the hash code of the value, if present, otherwise {@code 0} (zero) if no value is present.
     *
     * @return hash code value of the present value or {@code 0} if no value is present
     */
    @Override
    public int hashCode() {
        return Objects.hashCode(value);
    }

    /**
     * Returns a non-empty string representation of this {@code Optional} suitable for debugging.  The exact
     * presentation format is unspecified and may vary between implementations and versions.
     *
     * @return the string representation of this instance
     * @implSpec If a value is present the result must include its string representation in the result.  Empty and
     * present {@code Optional}s must be unambiguously differentiable.
     */
    @Override
    public String toString() {
        if (isPresent()) {
            return String.format("Optional.value{%s}", value);
        }
        return errorCode != null ? errorCode.toString() : "Optional.empty";
    }
}
